1. Technical Field
This invention relates to data communication systems. More particularly, this invention relates to a method and apparatus for bidirectional data transfer between a digital display and a computer.
2. Description of the Related Art
In today""s computing environment, the interface between a computer and a human is achieved by the interaction between a display and a human. Many I/O devices involved in a friendly user interface are connected together with a display for human interaction.
Existing cabling methods force all I/O devices connected to the computer itself with various kinds of cables and connectors, creating a difficulty with the cabling while occupying the space for the connectors. With an emerging digital data interface between a digital display and a computer, it is necessary to define a new signaling and cabling scheme which can ease all the cabling difficulties while saving the connector space.
Therefore, there is a need for a way to transfer all the necessary signals from various I/O devices to a computer by simply adding a backward channel interconnect via either a clock pair or by adding one more pair of data signals to the existing digital display interface.
Accordingly, it is the object of the present invention to provide a bidirectional data transfer between a digital display and a computer which doesn""t require a backward clock.
This object is achieved in accordance with the present invention by providing a method and apparatus for bidirectional data transfer between a computer and a display connected through a cable having a first end at the computer and a second end at the display.
In a preferred embodiment, the apparatus includes a transmitter located at the computer for transmitting a pixel clock and forward data aligned to the pixel clock to the receiver in a forward channel, and a receiver located at the display for receiving the pixel clock and the data transmitted from the transmitter and for transmitting backward data to the transmitter in a backward channel. The transmitter further includes an oversampling circuit for generating a plurality of oversampling clocks for sampling the backward data received from the receiver, each clock being equally spaced in phase from its adjacent clock signal.
In an alternative embodiment, the apparatus includes a transmitter located at the computer and a receiver located at the display. The transmitter comprises a first unit-gain buffer for taking a pixel clock for transmitting data as an input and generating a voltage at the first end of the cable as an output, and a first subtractor for subtracting the pixel clock from the voltage at the first end of the cable to recover data received backward. The receiver comprises a second unit-gain buffer for taking backward data to be transmitted to the transmitter as an input and generating a voltage at the second end of the cable as an output, and a second subtractor for subtracting the backward data from the voltage at the second end of the cable to recover the pixel clock transmitted from the computer.